Piston-reciprocating gas compressor

ABSTRACT

A drive shaft is driven by an electric motor in a motor casing. A crankshaft integrally connected with the drive shaft is provided in a crankcase. A piston is reciprocated by the crankshaft in a cylinder. A gas is introduced from the outside into the motor casing and forwarded into the crankcase. The gas is further guided into a space on the piston through a gas-guiding groove formed in the inner circumference of the cylinder. The piston moves up to compress the gas in the space while the piston closes the upper end of the gas-guiding groove, so that the gas is discharged to the outside.

This application claims priority from Japanese Application Serial No. 2005-238685 filed Aug. 19, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to a piston-reciprocating gas compressor compressing a gas by reciprocating a piston.

As shown in FIG. 2, a piston-reciprocating gas compressor is known, in which a discharge check valve 23 and a suction check valve 24 are provided at one side and the other side of a top wall 22 of a cylinder 21. On the discharge check valve 23 and suction check valve 24, a suction chamber 26 having an inlet 25 and a discharge chamber 28 having an outlet 27 are provided respectively. In a crankcase 29 under the cylinder 21, a crankshaft 31 is integrally connected to a drive shaft 30. A drive shaft 30 is driven by an electric motor 32 outside the crankcase 29, so that a piston 34 in the cylinder 21 is reciprocated by the crankshaft 31 via a piston rod 33. A gas such as N₂ sucked from the inlet 25 is introduced into a space on the piston 34 via the suction check valve 23, compressed and discharged via the discharge check valve 24 and outlet 27.

In such a piston-reciprocating gas compressor, with reciprocating movement of the piston 34, the gas introduced into the space on the piston 34 in the cylinder 21 is partially leaked around the piston 34 to flow back into the crankcase 29 and is released to air from a ventilating hole 35. If the gas is toxic, it will cause environmental contamination.

In a booster-type compressor in which a compressed gas is sucked and further compressed, a compression chamber is decompressed in a sucking step during restarting or non-load operation, so that a gas introduced into the crankcase 29 via the ventilating hole 35 flows between the outer circumference of the piston 34 and the inner circumference of the cylinder 21 into the space on the piston 34 and is mixed with a gas from the inlet 25 to make its concentration lower.

Furthermore, to cool the electric motor 32, it is necessary to provide a ventilating hole 40 in the motor casing 36 and to mount a blowing fan on the drive shaft 30 to carry out forced cooling. Thus, it is not possible to seal the electric motor completely thereby rendering noise to leak and/or making dusts in air and solid components remain in each part of the electric motor 32 and motor casing 36.

In a booster-type compressor in which a gas is introduced into a space on the piston 34 via the inlet 25 and suction check valve 34, compressed and discharged from the outlet 27 via the discharge check valve 24, torque fluctuation per one rotation becomes larger to increase electric current value of the electric motor 32 directly mounted to the crankcase 29.

To overcome the disadvantages in the conventional piston-reciprocating gas compressor, the ventilating hole 35 of the crankcase 29 is removed to seal the crankcase 29 and electric motor 32. If the crankcase 29 and electric motor 32 are sealed, temperature of the inside of the crankcase 29 and electric motor 32 rises to cause damage to the bearing 35,36 and seal 37 of the drive shaft 30 and crankshaft 31 resulting in deterioration or leakages of oil to decrease the performance and durability of the compressor.

SUMMARY OF THE INVENTION

In order to overcome the disadvantages in the prior art, it is an object of the invention to provide a piston-reciprocating gas compressor that overcomes the disadvantages involved by an electric motor mounted outside a crankcase.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparent from the following description with respect to an embodiment as shown in accompanying drawings wherein:

FIG. 1 is a vertical sectional view showing a gas compressor according to the present invention; and

FIG. 2 is a vertical sectional view of a conventional gas compressor.

DETAILED DESCRIPTION OF PREFERREN EMBODIMENT

FIG. 1 is an embodiment of a piston-reciprocating gas compressor according to the present invention.

A discharge check valve 3 is provided in a top wall 2 of a cylinder 1, and a discharge chamber 5 having an outlet 4 is formed on the top wall 2. The lower end of the cylinder 1 is connected to a sealed crankcase 6. A motor casing 8 having a gas-introducing hole 7 at the end is connected to one side of the crankcase 6 via gas-guiding holes 9,9.

A motor 10 is provided in the motor casing 8, and a drive shaft 11 is integrally formed with a crankshaft 13 pivotally mounted in bearings 12,12 in the crankcase 6.

The end of a piston rod 15 of a piston 14 in the cylinder 1 is pivotally mounted to the crankshaft 13 via a bearing 16.

There is formed a gas-guiding groove 17 in the inner surface of the cylinder 1. The lower end of the gas-guiding groove 17 communicates with the inside of the crankcase 6. When the piston 14 is in the lowest position, the upper end of the gas-guiding groove 17 communicates with a space on the piston 14 in the cylinder 1, while the upper end of the gas-guiding groove is closed by the piston 14 and a piston ring as soon as the piston 14 moves up.

The discharge check valve 3 does not open by a compressed gas in the crankcase 6, but is set to open when a gas in the space in the cylinder 1 is compressed by moving up the piston 14.

The piston 14 is reciprocated by the drive shaft 11. Then an ordinary pressure gas or a compressed gas such as N₂ in the crankcase 6 is forwarded to the space on the piston 14 via the gas-guiding groove 17, compressed and discharged via the discharge check valve 3 and a discharge hole 4.

Instead of the gas-guiding groove 17, an intake check valve may be used in the piston 14.

The foregoing merely relate to an embodiment of the invention. Various changes and modifications may be made by a person skilled in the art without departing from the scope of claims wherein: 

1. A piston-reciprocating gas compressor comprising: an electric motor; a motor casing including the electric motor and having a gas-introducing hole through which a gas is introduced from an outside: a drive shaft driven by the electric motor and extending in the motor casing; a crankshaft integrally connected to the drive shaft; a crankcase including the crankshaft and having a gas-guiding hole to allow the motor casing to communicate with the crankcase; a piston reciprocated by the crankshaft; and a cylinder including the piston and having a gas-guiding groove in a lower part of an inner circumference to allow the crankcase to communicate with a space on the piston in the cylinder when the piston is in a lower position so that the gas in the crankcase is guided into the space through the gas-guiding groove between an outer circumference of the piston and the inner circumference of the cylinder, an upper end of the gas-guiding groove being closed when the piston moves up so that the gas in the space on the piston is compressed and discharged from the cylinder.
 2. The piston-reciprocating gas compressor according to claim 1 wherein the gas is discharged through a discharge check valve in a wall of the cylinder. 